1. An image forming apparatus for making gray-scale images, said image forming apparatus comprising:
a dot status detector configured to detect an occurrence in which a dot exists at a focus dot position and no dot exists at both positions immediately adjacent to the focus dot position in the main scanning direction; and
a density adjuster configured to convert a writing level of the dot at the focus dot position to a first value when the dot status detector detects the occurrence and to convert the writing level of the dot at the focus dot position to a second value, different from the first value, when the dot status detector does not detect the occurrence.
2. The image forming apparatus as defined in claim 1, further comprising:
a dot phase adjuster configured to expand the dot in a direction right of a center of the dot when the dot status detector detects the occurrence and configured to expand the dot in a direction left of the center of the dot when the dot status detector does not detect the occurrence.
3. An image forming apparatus for making gray-scale images, said image forming apparatus comprising:
dot status detecting means for detecting an occurrence in which a dot exists at a focus dot position and no dot exists at both positions immediately adjacent the focus dot position in the main scanning direction; and
density adjusting means for converting a writing level of the dot at the focus dot position to a first value when the dot status detecting means detects the occurrence and for converting the writing level of the dot at the focus dot position to a second value, different from the first value, when the dot status detecting means does not detect the occurrence.
4. The image forming apparatus as defined in claim 3, further comprising:
dot phase adjusting means for expanding the dot in a direction right of a center of the dot when the dot status detecting means detects the occurrence and for expanding the dot in a direction left of the center of dot when the dot status detecting means does not detect the occurrence.
5. A method for forming gray-scale images, said method comprising:
detecting whether an occurrence exists in which a dot exists at a focus dot position and no dot exists at both positions immediately adjacent the focus dot position in the main scanning direction; and
converting a writing level of the dot at the focus dot position to make a smooth gray-scale transition to a first level when the detecting step detects the occurrence; and
converting the writing level of the dot at the focus dot position to a second value different from the first value, when the detecting step does not detect the occurrence.
6. The method as defined in claim 5, further comprising the step of:
expanding the dot in a direction right of a center of the dot when the detecting step detects the occurrence, and expanding the dot in a direction left of the center of the dot when the detecting step does not detect the occurrence.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A frequency detection apparatus, comprising:
a constant current generator, arranged for providing a constant current to a voltage output terminal;
a first capacitor, coupled between the voltage output terminal and a first reference voltage;
a first transistor, having a first connection terminal, a control terminal, and a second connection terminal, wherein the first connection terminal of the first transistor is coupled to the voltage output terminal, and the control terminal of the first transistor is coupled to an input signal;
a second capacitor, coupled between the second connection terminal of the first transistor and the first reference voltage; and
a second transistor, having a first connection terminal, a control terminal, and a second connection terminal, wherein the first connection terminal of the second transistor is coupled to the second connection terminal of the first transistor, the second connection terminal of the second transistor is coupled to the first reference voltage, and the control terminal of the second transistor is coupled to an inverted input signal;
wherein a voltage output of the voltage output terminal changes along with an input signal frequency of the input signal, and the constant current generator comprises:
a first resistor, coupled between a second reference voltage and the voltage output terminal;
a third transistor, having a first connection terminal, a control terminal and a second connection terminal, wherein the first connection terminal is coupled to the voltage output terminal, and the second connection terminal is coupled to the second reference voltage;
a fourth transistor, having a first connection terminal, a control terminal and a second connection terminal, wherein the first connection terminal of the fourth transistor is coupled to the control terminal of the third transistor and the control terminal of the fourth transistor, and the second connection terminal of the fourth transistor is coupled to the second reference voltage;
a fifth transistor, having a first connection terminal, a control terminal and a second connection terminal, wherein the first connection terminal of the fifth transistor is coupled to the first connection terminal of the fourth transistor;
an amplifier, having a positive input terminal, a negative input terminal and an output terminal, wherein the positive input terminal is coupled to the voltage output terminal, the negative input terminal is coupled to the second connection terminal of the fifth transistor, and the output terminal is coupled to the control terminal of the fifth transistor; and
a second resistor, coupled between the second connection terminal of the fifth transistor and the first reference voltage.
2. The frequency detection apparatus of claim 1, wherein the voltage output of the voltage output terminal is inversely proportional to the input signal frequency of the input signal.
3. The frequency detection apparatus of claim 1, further comprising:
a comparator, having a first input terminal and a second input terminal, wherein the first input terminal is coupled to the voltage output terminal, and the second input terminal is coupled to a predetermined voltage corresponding to a predetermined frequency;
wherein the comparator is arranged to determine whether the input signal frequency of the input signal exceeds the predetermined frequency.
4. The frequency detection apparatus of claim 1, wherein the input signal is a pulse frequency modulation (PFM) signal outputted by a modulation unit which performs a pulse frequency modulation.
5. The frequency detection apparatus of claim 1, wherein the voltage output of the voltage output terminal is inversely proportional to a value of the second capacitor.
6. A frequency detection apparatus, comprising:
a constant current generator, arranged for providing a constant current to a voltage output terminal, wherein the constant current generator comprises:
a first resistor, coupled between a second reference voltage and the voltage output terminal;
a first transistor, having a first connection terminal, a control terminal and a second connection terminal, wherein the first connection terminal is coupled to the voltage output terminal, and the second connection terminal is coupled to the second reference voltage;
a second transistor, having a first connection terminal, a control terminal and a second connection terminal, wherein the first connection terminal of the second transistor is coupled to the control terminal of the first transistor and the control terminal of the second transistor, and the second connection terminal of the second transistor is coupled to the second reference voltage;
a third transistor, having a first connection terminal, a control terminal and a second connection terminal, wherein the first connection terminal of the third transistor is coupled to the first connection terminal of the second transistor;
an amplifier, having a positive input terminal, a negative input terminal and an output terminal, wherein the positive input terminal is coupled to the voltage output terminal, the negative input terminal is coupled to the second connection terminal of the third transistor, and the output terminal is coupled to the control terminal of the third transistor; and
a second resistor, coupled between the second connection terminal of the third transistor and the first reference voltage; and
a frequency-voltage conversion unit, arranged for receiving an input signal, an inverted input signal and the constant current, and generating a voltage output at the voltage output terminal according to the input signal, the inverted input signal and the constant current;
wherein there is a predetermined proportion relationship between the voltage output and an input signal frequency of the input signal.
7. The frequency detection apparatus of claim 6, wherein the predetermined proportion relationship is an inverse proportion relationship.
8. The frequency detection apparatus of claim 6, further comprising:
a comparator, having a first input terminal and a second input terminal, wherein the first input terminal is coupled to the voltage output terminal, and the second input terminal is coupled to a predetermined voltage corresponding to a predetermined frequency;
wherein the comparator is arranged to determine whether the input signal frequency of the input signal exceeds the predetermined frequency.
9. The frequency detection apparatus of claim 6, wherein the input signal is a pulse frequency modulation (PFM) signal outputted by a modulation unit which performs a pulse frequency modulation.